Studying the leaching mechanism of spent SCR catalyst with different leaching agents (NaOH, H₂SO₄, HCl and HNO₃) using DFT calculations

The leaching mechanism of the spent selective catalytic reduction (SCR) catalyst was investigated by density functional theory (DFT) calculations and experiments. Three models, namely V2O5/TiO2, WO3-V2O5/TiO2, and WO3/TiO2, were created to simulate the spent SCR catalyst. Interaction between the surface clusters and the leaching agents of NaOH, H2SO4, HCl and HNO3 was investigated by DFT calculations. The adsorption site was determined through electrostatic potential and adsorption energy. The calculations showed that NaOH tended to be adsorbed on V and W atoms. H2SO4, HCl and HNO3 tended to be adsorbed on specific O atoms. H2SO4 dissociated on all three models, HCl dissociated on V2O5/TiO2 and WO3-V2O5/TiO2, while HNO(3 )dissociated only on V2O5/TiO2. The order of leaching ability among leaching agents was NaOH > H2SO4 > HCl > HNO3. Ex-periments showed that the leaching ratios of V and W in NaOH solution were 82.4% and 54.3%. In acid solution, the leaching ratio of V was 69.0% for H2SO4, 52.5% for HCl, and 42.2% for HNO3, while W was hardly leached out. After acid leaching, the change in the TiO2 lattice parameter was greater than that after alkaline leaching. The experimental results were found to be consistent with the calculations.